WOT Miss that Won't Go Away

[spayne83]

I recently did a plug chop to try to figure out what is causing the WOT miss between 4000-6500.

This is what the new plus looked like gapped at .32





Only 1 and 4 had any color on them

Here were the original plugs





They were all tan ish at the top of the insulator with maybe a tinge of yellow.

After that I tried fiddling with the ignition advance as I thought that I saw a hint of aluminum on some of the plugs I pulled but retarding the timing didn't solve the problem, however it did make it a little less noticeable. I also put on EMGO megaphone mufflers because I thought that my turnouts had no baffles and thus no backpressure. (Side note: Always check that dimensions of the parts prior to buying then so you do not have to mod them to make them fit.)

Today I rejetted from 145 to 142.5 since I thought that maybe I was a little too rich. Same problem, but a little less pronounced. Then I put in a gallon of 91 octane and it made it a little bit better and also made 6500-8000 pull really hard. I rode with the carb sync gauges on and at WOT I am pulling almost 0 vacuum with 16-18 in on full decel and 8 in on cruise.

I don't know if I have introduced too many variables but I am trying to do everything one change at a time, so that I am not shooting completely in the dark.

[IanDMacDonald]

Pods and mufflers justified a 145 main, let-alone a 142.5 main? My suggestion to like anybody else willbsay is go back to stock settings, and tune from there. Remember, you also have an adjustable needle to play with. I have a modified box, and prior to my stock exhaust, 4-2 turn-outs, and I had 140's.

[mmaddix]

What intake do you use? Airbox? Pod filters?

I had a stumble at high rpms when I installed an airbox on my bike. I am running no muffler so I have no back pressure. With the airbox and no muffler, I had to adjust the fuel air mixture extremely rich in order to get it to run. And at high rpms it would stumble. Once i put pod filters back on I had to lean the fuel air mixture so it would run well. Now I have power at all rpms. These bikes need that back pressure. Once I put my new exhaust on then I will put the shoebox back on and I'm sure it will be fine.

Hope this helps.

I noticed in your tag you say you have el cheapo pods they might cover an air hole on the carbs. There is a post about modifying the fillers to not block the hole.

[mack]

plugs

If you can take a flashlight and shine it down to the bottom of the porclin. Look for a very thin darker ring. This will tell you if your lean or rich on the mains. No ring is lean, fat ring or fully dark on the bottom your rich. No need to do the chop with this inspection just ride it normally and check the colours.
There is a science to reading plugs, they can tell you a wide variety of info on your machine. Idle, pilot and main circuits, timing etc.

[James England]

Two and three appear to be running very weak. You have introduced several variables into the diagnosis on this problem. Are you running with standard airbox?

[TopCatGr58]

Hey James,

His signature

El Cheapo Pod Filter Mod w/ EMGO Pods, Coil Repower w/ Dyna Coils, Accell Wires and Side Gapped Plugs, 78 Mech Advance, 4-2 Turnouts

shows the Pods with the Pod Mod mounts.

Spayne, with those white plugs, it still looks lean, and you actually leaned the mains from 145 to 142.5?? Okay, the plug chop photos were from a few days ago, and then you said you put on mufflers with baffles to increase backpressure, you also retarded the timing a little. But you didn't do a plug chop with the new mufflers on, so you don't really know if you had changed the exhaust flow enough to richen it up?

You say the stumble happens in the 4 - 6k range, that's pretty much when you're getting on the mains, especially when you say you're using WOT, the vac. slides should be rising quite a bit to let in as much fuel as the engine can use. I don't recall what your float settings were also?

I disagree with going back to stock setting/jetting, your plugs already show that you are quite lean with the 145's..albeit that was with your open 4-2's, but even with the new Emgo mufflers and baffles, you still experienced the problem/stumble with the 142.5's. Using the 91 octane fuel helped to slow down the burn rate, so it could have a little more time to burn the fuel, so even though it may still be lean, it burned it slower so you had a decent response in the 6-8k range...along with the now retarded timing.

Also, don't recall what pilot jets you have, and how many turns out they are at?? The Pilots still provide some input/flow even when you're getting into the mains. You showed some color with the plugs checked with just idling and you had a little color so they are probably close anyways.

Keep at it. I haven't seen many posts about folks being successful with raising the slide needle 1 notch richer....they usually found it too rich and gets things fixed once they get the proper needed jet sizes.

T.C.

[spayne83]

I just swapped the 145 jets back in and replaced the emgo filters with k&n filters. The miss is almost gone with 91 octane and now only lasts from 6000 to 7000. I am noticing something weird going on with the vacuum. I synced all the cylinders at idle, but they soon lost the sync with #2 idling with less vacuum than the rest. They also don't read the same when riding. I'll try to take a video.

[skids]

I just swapped the 145 jets back in and replaced the emgo filters with k&n filters. The miss is almost gone with 91 octane and now only lasts from 6000 to 7000. I am noticing something weird going on with the vacuum. I synced all the cylinders at idle, but they soon lost the sync with #2 idling with less vacuum than the rest. They also don't read the same when riding. I'll try to take a video.

What do you mean? Vacuum synch is for near idling rpms. If you try and adjust throttle plates at any other higher rpms your idle will be screwed up.

[spayne83]

Right. I set the vacuum sync at idle and left th gauges on while I rode and the vacuum did not stay synced.